Scott Hanselman recommends teaching systems thinking over technical coding:
I told this young person to try not to focus on the syntax of C# and the details of the .NET Framework, and rather to think about the problems that it solves and the system around it.
This advice was .NET specific, but it can also apply to someone learning Rails 3 talking to someone who knows Rails 5, or someone who learned original Node and is now reentering the industry with modern JavaScript and Node 12.
Do you understand how your system talks to the file system? To the network? Do you understand latency and how it can affect your system? Do you have a general understanding of "the stack" from when your backend gets data from the database makes anglebrackets or curly braces, sends them over the network to a client/browser, and what that next system does with the info?
Squeezing an analogy, I'm not asking you to be able to build a car from scratch, or even rebuild an engine. But I am asking you for a passing familiarity with internal combustion engines, how to change a tire, or generally how to change your oil. Or at least know that these things exist so you can google them.
This is why I'm a fan of Hanselman. He's right. Learning technical skills is easy; learning how to think is hard.